Packaging refers to a set of technologies that connect integrated circuits (ICs) with electronic systems. The packaging may include on-chip interconnections and chip-to-printed circuit board interconnections. One form of the packaging may involve three basic processes: die attach, wire bond, and encapsulation.
The die attach process provides mechanical adhesion of a chip to its intended substrate (e.g., a printed circuit board, interconnecting substrate, etc.). The chip may be picked up (e.g., by a machine) from a wafer sawed off in an earlier process. The bottom surface of the chip is often laminated with an adhesive film formed at the wafer level. The chip is then placed precisely to an intended location and the adhesive film is cured (e.g., baked) to complete the die attach process.
Next, the chip is attached to a printed circuit board or another electronic system in the wire bond process. The wire bond process requires connecting bond wires between bonding pads of the chip to contact points on the printed circuit board. During the process, a wire bond machine welds the bond wires between the bonding pads and the contact points by using the technique of ultrasonic, thermosonic, or thermocompression bonding. In the encapsulation process, the die (e.g., and/or the bonding wires and/or the contact points) is enclosed is an encapsulant to protect itself from mechanical damage during handling and additional processing.
A stacked die configuration, whereby multiple dies are placed on top of another, may be used to develop more powerful components while decreasing the size (e.g., the width, length, and/or height) of the components (e.g., or a package enclosing the components). A number of methods are currently used to reduce the height of the package. A silicon spacer, a film spacer, a spacer paste, and/or a film on wire layer (FOW) are currently used in the application of a stacked die or multi die packing process.
FIG. 1 is a cross sectional view of a die spacer 114 formed between a first die 104 and a second die 118. As illustrated in FIG. 1, a bottom surface of the first die 104 (e.g., with one or more integrated circuits) is laminated with an adhesive film 106 before the first die 104 is sawed off from the wafer. As explained earlier in the die attach process, the first die 104 is picked up and placed above a mounting base 102 (e.g., a die attach pad of a leadframe, a first conductive area of the interconnecting substrate, etc.).
Then, a wire bonding machine (e.g., a capillary wire bonding machine) may be used to connect bonding wires (e.g., a bonding wire 112A, a bonding wire 112B, etc.) between bonding pads (e.g., a bonding pad 108A, a bonding pad 108B, etc.) and contact points (e.g., a bonding finger 110A, a bonding finger 110B, etc.) located on leads of the leadframe or a second conductive area of the interconnecting substrate electrically detached from the first conductive area. The bonding wires being used are often exposed to other components and/or environments without any protection.
Next, the die spacer 114 (e.g., a silicon spacer) is attached above the first die 104. As shown in FIG. 1, the die spacer 114 is designed to leave an extra room above the peak of the bonding wires such that the second die 118 does not touch, short, or damage the bonding wires below. The die spacer 114 also comes with an adhesive film 116 to secure itself above the first die 104. Then, the second die 118 is adhered on top of the die spacer 114 using an adhesive film 120.
Because the die spacer 114 has to clear the bonding wires, the height of the die spacer 114 (e.g., which may range from between 50 and 100 micrometers) plus the height of the adhesive film 116 (e.g., which is its height ranging from 10 to 50 micrometers) of the second die 118 have to added to the total height of the package. The added heights could significantly add to the size of the package when the package has a large number of stacked dies (e.g., where the number is often three to five but may be as much as ten or more). Furthermore, an extra labor and/or time may be required to form and/or implement the die spacer 114, thus decreasing the throughput and/or increasing the production cost of the packaging process.
FIG. 2 is a cross sectional view of a film on wire layer 214 formed between a first die 204 and a second die 216. The film on wire layer 214 is used in place of the die spacer 114 to separate the second die 216 from the bonding wires below (e.g., 212A, 212B, etc.). Although the film on wire layer 214 eliminates the adhesive film which would have been laminated at the bottom surface of the second die 216, the film on wire layer 214 has to be formed in such a height to clear the bonding wires (e.g., a bonding wire 212A, a bonding wire 212B, etc.) which are not protected. As in FIG. 1, the extra height required in the film on wire layer 214 (FOW) may add to the total height of the package. In addition, the extra time, labor and cost to apply the amount of the film on wire layer 214 may make the packing process inefficient and/or unproductive.